The efficacy of virginity pledges has been extensively studied. Some studies have found that virginity pledges may be effective at delaying vaginal intercourse, but that they are ineffective in reducing the incidence of sexually transmitted infections (STIs) because pledgers may replace vaginal intercourse with other sexual activities, such as oral sex and anal sex;[1][2] other research, however, has suggested no such substitution among pledgers, though pledgers may partake in vaginal or oral sex.[3] Virginity pledges may also reduce the likelihood of contraceptive use once pledgers decide to engage in sex.[1] Though studies have reported this and found that pledgers are more likely to remain virgins by age 25 than those who do not pledge and that those who do become sexually active report fewer sexual partners,[1][2] at least one study found no difference in the sexual behavior of pledgers and non-pledgers after controlling for pre-existing differences between the groups.[3]

On August 22, the department suspended SRT's $75,000 federal grant until it submitted a "corrective action plan." In 2006, a corrective action plan was accepted by the department, the lawsuit was dismissed and SRT received its Federal Funding.

Virginity pledge programs take a variety of stances on the role of religion in the pledge: some use religion to motivate the pledge, putting Biblical quotes on the cards, while others use statistics and arguments to motivate the pledge. Advocacy of virginity pledges is often coupled with support for abstinence-only sex education in public schools. Advocates argue that any other type of sexual education would promote sex outside of marriage, which they hold to be immoral and risky.

There have been numerous peer-reviewed studies of virginity pledges with varying results. Four of the five peer-reviewed virginity pledge studies and the non-peer-reviewed study discussed below use the same federal data, the National Longitudinal Study of Adolescent Health (Add Health), in which 13,000 adolescents were interviewed in 1995, 1996, and 2000. The other peer-reviewed study used a study of virginity pledges in California.

The first peer-reviewed study of virginity pledgers (by sociologists Peter Bearman of Columbia and Hannah Brueckner of Yale) found that in the year following their pledge, some virginity pledgers are more likely to delay sex than non-pledgers; when virginity pledgers do have sex, they are less likely to use contraception than non-pledgers.[1] This study found, however, that virginity pledges are only effective in high schools in which about 30% of the students had taken the pledge, meaning that they are not effective as a universal measure. Their analysis was that identity movements work when there is a critical mass of members: too few members, and people don't have each other for social support, and too many members, and people don't feel distinctive for having taken the pledge. This study was criticized for not being able to conclude causality, only correlation, a criticism which applies to all studies of virginity pledges thus far.[7]

A second peer-reviewed study, also by Bearman and Brueckner, looked at virginity pledgers five years after their pledge, and found that the pledgers have similar proportions of sexually transmitted infections (STIs) and at least as high proportions of anal and oral sex as those who have not made a virginity pledge. They deduced that there was substitution of oral and anal sex for vaginal sex among the pledgers, although the data for anal sex without vaginal sex reported by males did not reflect this directly.[1][2] This study also estimated that male pledgers were 4.1 times more likely to remain virgins by age 25 than those who did not pledge (25% vs. 6%), and estimated that female pledgers were 3.5 times more likely to remain virgins by age 25 than those who did not pledge (21% vs. 6%). The study also noted that those who pledge yet became sexually active reported fewer partners and were not exposed to STI risk for as long as nonpledgers.[1][2]

A third peer-reviewed study — by Melina Bersamin and others at Prevention Research Center, in Berkeley, California — found that adolescents who make an informal promise to themselves not to have sex will delay sex, but adolescents who take a formal virginity pledge do not delay sex.[8]

A fourth peer-reviewed study — by Harvard public health researcher Janet Rosenbaum published in the American Journal of Public Health in June 2006 — found that over half of adolescents who took virginity pledges said the following year that they had never taken a pledge.[9] This study showed that those who make the pledge but have sex are likely to deny ever pledging; and many who were sexually active prior to taking the pledge deny their sexual history, which, it is speculated, may cause them to underestimate their risk of having STIs.

A fifth peer-reviewed study, also by Janet Rosenbaum published in the journal Pediatrics in 2009,[3] found no difference in sexual behavior of pledgers and similar non-pledgers five years after pledging, but found pledgers were 10 percentage points less likely to use condoms and 6 percentage points less likely to use birth control than similar non-pledgers. Rosenbaum's study was innovative for using Rubin causal model matching, instead of relying on regression analysis, which makes potentially untrue parametric assumptions. According to Rosenbaum, past research findings that virginity pledgers delayed sex may have been affected by their statistical method's inability to adjust fully for pre-existing differences between pledgers and non-pledgers: pledgers are much more negative towards premarital sex prior to even taking the pledge, so would be predicted to delay sex even if they hadn't taken the pledge. Comparing pledgers with similar non-pledgers is the only way to be certain that the effect comes from the pledge rather than the pre-existing greater beliefs of pledgers that sexuality should be restrained to the matrimonial context.[10]

"Believing that true love waits, I make a commitment to God, myself, my family, my friends, my future mate, and my future children to a lifetime of purity including sexual abstinence from this day until the day I enter a Biblical marriage relationship."

True Love Waits recent pledge (2009):

"I am making a commitment to myself, my family, and my Creator, that I will abstain from sexual activity of any kind before marriage. I will keep my body and my thoughts pure as I trust in God's perfect plan for my life."
(quote on card) "It is God's will that you should be sanctified: that you should avoid sexual immorality; that each of you should learn to control his/her own body in a way that is holy and honorable." 1 Thess 4:3-4